Undercutting knives that are in current use on sod cutting machines are thoroughly described by F. J. Ditter's U.S. Pat. No. 3,034,586, issued May 15, 1962, and by Brouwer's U.S. Pat. Nos. 3,509,944, issued May 5, 1970, 4,015,666, issued Apr. 5, 1977, and 4,018,287, issued Apr. 19, 1977. Such knives are intended to be sharpened several times before being discarded, which requires their removal from the sod cutting machine. Such removal customarily requires the removal of several threaded fasteners, and takes an appreciable amount of time that could otherwise be spent cutting sod. This lost time, plus the time spent in sharpening the knife, is very costly for sod producers.
Additionally, unless the sharpening is done very carefully and accurately, the geometry of the knive will be changed, resulting in less than optimum performance. This is particularly true of undercutting knives that are manufactured as an integral unit with the side cutting knives. In these designs, correct sharpening is quite difficult in the corner where the side knives join the undercutting knive.
Undercutting knives are manufactured from steel and are hardened to minimize wear. Since several pounds of steel may be used for each knife, and since the life of a knife is limited, at best, the knives are customarily made from an inexpensive carbon steel such as C-1095. This steel lacks the alloying elements that impart toughness along with high hardness. In order to prevent excessive breakage, then, undercutting blades made from steel such as C-1095 are hardened only moderately. As an example, many blades are manufactured to a hardness of Rc-45. Such blades are not readily broken, but will lose their cutting edge much more rapidly than a harder blade would.
Accordingly, it is an object of the present invention to provide an undercutting knife for a sod cutting machine which includes a blade which contains a very small amount of steel and which therefore can be manufactured from steel of higher quality and greater unit cost than is presently the case. Another object of the invention is to provide an undercutting knife which includes a blade which can be very rapidly removed from the machine and replaced. Another object of the invention is to provide an undercutting knife which includes a blade which is very low in cost, and which can economically be discarded after use, rather than sharpened. Another object of the invention is to provide an undercutting knife with a blade which is unchanging in geometry and cutting depth. Other advantages will be apparent from the following description.